The Evolution: Prompt Engineering is Dead?

The 2025-2026 Paradigm Shift

• Gartner (July 2025): “Context engineering is in, and prompt engineering is out”
• The Problem with Prompts Alone:
  • LLMs have finite context windows (4K-200K tokens)
  • Flooding with irrelevant instructions dilutes important information
  • Longer/trickier prompts yield diminishing returns
  • Prompts cannot compensate when model lacks situational data

Key Insight

“Prompt engineering is what you do inside the context window. Context engineering is how you decide what fills the window.”

What is Context Engineering?

Definition (Andrej Karpathy, 2025)

“Context engineering is the delicate art and science of filling the context window with just the right information for each step.”

It’s a System-Level Discipline

• Not just prompts - Managing everything the model sees at runtime:
  • Retrieved documents (RAG)
  • System state and memory
  • Prior outputs and conversation history
  • Tool definitions and schemas
  • Results from external APIs
  • User preferences and permissions

Why Context Engineering Emerged

LLM Limitations Drive the Need

1. LLMs are Stateless
   • They don’t “remember” unless you reinsert memory into context
2. LLMs Hallucinate
   • Contextual grounding through external data reduces this
3. LLMs are Brittle
   • Prompt-only approaches don’t scale or generalize

Industry Evidence (LangChain 2025 Report)

• 57% of organizations have AI agents in production
• 32% cite quality as top barrier
• Most failures traced to poor context management, not LLM capabilities

Context Engineering: Core Components

The Context Stack

1. System Instructions - Role, constraints, output format
2. Retrieved Knowledge - RAG, vector search results
3. Memory - Conversation history, user preferences
4. Tool Definitions - Available functions, API schemas
5. Examples - Few-shot demonstrations
6. Current Task - The actual user request

Key Principle: Context is a Resource

• Treat context window like memory allocation
• Every token has a cost (latency, accuracy, price)
• Prioritize high-signal information
• Dynamically adjust based on task

Context Engineering Best Practices

Design Principles

1. Relevance Filtering: Only include what’s needed for the current step
2. Recency Weighting: Recent context often more relevant
3. Compression: Summarize long histories
4. Chunking: Break large documents intelligently
5. Caching: Reuse computed context where possible

Anti-Patterns to Avoid

• Stuffing everything into context “just in case”
• Static prompts that don’t adapt to task
• Ignoring token limits until truncation occurs
• No separation between instruction and data

Context Engineering Resources

Essential Reading

• Context Engineering: The Definitive 2025 Guide
• Context Engineering Guide - Prompting Guide
• From Prompt Engineering to Context Engineering
• Context Engineering: A Complete Guide 2026
• Context Engineering vs Prompt Engineering

Key Figures

• Tobi Lütke (Shopify CEO): Popularized the term
• Andrej Karpathy: “Delicate art and science” definition

The DSPy Revolution

What is DSPy?

• Framework for programming—not prompting—language models (Stanford NLP)
• Abstracts prompts into modular Python code
• Automatically optimizes prompts using ML techniques

The Core Idea

Instead of:

prompt = "You are a helpful assistant. Please summarize..."  # Manual trial & error

With DSPy:

class Summarizer(dspy.Signature):
    """Summarize the given text concisely."""
    text = dspy.InputField()
    summary = dspy.OutputField()

# Optimizer finds the best prompt automatically!

How DSPy Optimization Works

The Process

1. Define Behavior Declaratively - Use Signatures to specify input/output
2. Provide Training Examples - Small set of examples with expected outputs
3. Define a Metric - How to measure success
4. Run Optimizer - AI automatically discovers optimal prompts

Key Optimizers

DSPy: Real Results

Automated Improvement

• One optimizer raised evaluation from 51.9% to 63.0% automatically
• HotPot QA: 18.42% relative improvement without manual prompt editing

Why This Matters

• Scales AI Development: Automates the most time-consuming aspect
• Model Switching: Change from GPT-4 to Llama = config change + re-optimize
• Reproducibility: Systematic optimization vs. ad-hoc prompt tweaking

Resources

• DSPy Framework
• GitHub: stanfordnlp/dspy
• DSPy Tutorial 2025

Modern Prompt Structures (2026)

Beyond Simple Instructions

1. XML-Tagged Sections (Claude preferred)

<context>You are analyzing customer feedback</context>
<instructions>Classify sentiment and extract key themes</instructions>
<examples>...</examples>
<input>{{user_input}}</input>

2. Structured Output Enforcement

Respond in JSON format:
{"sentiment": "positive|negative|neutral", "themes": [...]}

3. Chain-of-Thought Triggers

Think step by step. Show your reasoning before the final answer.

The Shift to Structured Outputs (2025-2026)

Why Structured Outputs Matter

• Reliability: Guarantees valid JSON/schema output every time
• Integration: Direct parsing into application code
• Validation: Schema enforcement prevents malformed responses
• Industry Adoption: Every major API now supports this natively

The Problem with Unstructured Output

# Old approach - brittle parsing
response = llm("Extract name and email from: John at john@example.com")
# Response: "The name is John and email is john@example.com"
# Now you need regex or more LLM calls to parse this

Structured Outputs: Implementation

OpenAI JSON Mode

from openai import OpenAI
client = OpenAI()

response = client.chat.completions.create(
    model="gpt-4o-2026-01-01",
    response_format={"type": "json_object"},
    messages=[
        {"role": "system", "content": "Extract data as JSON with keys: name, email"},
        {"role": "user", "content": "John Smith can be reached at john@example.com"}
    ]
)
# Guaranteed valid JSON: {"name": "John Smith", "email": "john@example.com"}

Anthropic Tool Use for Structured Output

import anthropic
client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    tools=[{
        "name": "extract_contact",
        "description": "Extract contact information",
        "input_schema": {
            "type": "object",
            "properties": {
                "name": {"type": "string"},
                "email": {"type": "string", "format": "email"}
            },
            "required": ["name", "email"]
        }
    }],
    tool_choice={"type": "tool", "name": "extract_contact"},
    messages=[{"role": "user", "content": "Contact: John Smith, john@example.com"}]
)

Function Calling: Connecting LLMs to Tools

What is Function Calling?

• LLM decides when to call a function and what arguments to pass
• You execute the function, return results to LLM
• LLM incorporates results into response

Common Use Cases

Industry Reality

• 80%+ of production AI apps use function calling
• Foundation for all AI agents and assistants
• MCP (Model Context Protocol) builds on this pattern

Function Calling: Amazon Bedrock Example

Tool Definition with Converse API

import boto3
import json

bedrock = boto3.client('bedrock-runtime', region_name='us-east-1')

tools = [{
    "toolSpec": {
        "name": "get_stock_price",
        "description": "Get current stock price for a ticker symbol",
        "inputSchema": {
            "json": {
                "type": "object",
                "properties": {
                    "ticker": {"type": "string", "description": "Stock ticker symbol"}
                },
                "required": ["ticker"]
            }
        }
    }
}]

response = bedrock.converse(
    modelId="anthropic.claude-sonnet-4-20250514-v1:0",
    messages=[{"role": "user", "content": [{"text": "What's Apple's stock price?"}]}],
    toolConfig={"tools": tools}
)
# LLM returns: tool_use with {"ticker": "AAPL"}

The Economics of LLM Calls

Token Costs Add Up Fast

The Caching Opportunity

• System prompts often 1000-5000 tokens
• Repeated across every request
• With 10,000 requests/day = massive waste

Anthropic Prompt Caching

How It Works

import anthropic
client = anthropic.Anthropic()

response = client.messages.create(
    model="claude-sonnet-4-20250514",
    max_tokens=1024,
    system=[
        {
            "type": "text",
            "text": "You are a customer service agent for Acme Corp...[long instructions]...",
            "cache_control": {"type": "ephemeral"}  # Cache this block
        }
    ],
    messages=[{"role": "user", "content": "How do I return an item?"}]
)

Cost Savings

• Cache write: 25% more than base input price
• Cache read: 90% discount on cached tokens
• Break-even: ~2 requests with same cached content
• TTL: 5 minutes (ephemeral), extendable with activity

Prompt Caching Strategies

What to Cache

1. System instructions - Role definitions, rules, formatting
2. Few-shot examples - Consistent across requests
3. Retrieved documents - RAG results used multiple times
4. Tool definitions - Same tools across conversations

Caching Architecture Pattern

┌─────────────────────────────────────────┐
│  Cached (5000 tokens) - $0.30/M reads   │
│  ┌─────────────────────────────────┐    │
│  │ System prompt + Rules           │    │
│  │ Few-shot examples               │    │
│  │ Tool definitions                │    │
│  └─────────────────────────────────┘    │
├─────────────────────────────────────────┤
│  Dynamic (500 tokens) - Full price      │
│  ┌─────────────────────────────────┐    │
│  │ User message                    │    │
│  │ Conversation history            │    │
│  └─────────────────────────────────┘    │
└─────────────────────────────────────────┘

The Evaluation Gap

Why This Matters

• 58% of AI teams lack systematic prompt evaluation (2025 survey)
• “Vibe checking” doesn’t scale
• Production failures often traced to untested prompt changes

What to Evaluate

1. Accuracy: Does it produce correct outputs?
2. Consistency: Same input → same output quality?
3. Edge cases: How does it handle unusual inputs?
4. Safety: Does it follow guardrails?
5. Cost: Token usage within budget?

Prompt Testing Frameworks

Unit Testing Prompts

import pytest
from your_llm_client import generate_response

class TestSentimentPrompt:
    """Test suite for sentiment classification prompt"""

    def test_positive_sentiment(self):
        result = generate_response("I absolutely love this product!")
        assert result["sentiment"] == "positive"
        assert result["confidence"] > 0.8

    def test_negative_sentiment(self):
        result = generate_response("This is the worst experience ever")
        assert result["sentiment"] == "negative"

    def test_neutral_edge_case(self):
        result = generate_response("The product arrived on Tuesday")
        assert result["sentiment"] == "neutral"

    def test_empty_input_handling(self):
        result = generate_response("")
        assert "error" in result or result["sentiment"] == "unknown"

Evaluation Metrics and Tools

Key Metrics

Popular Tools (2026)

• Promptfoo: Open-source prompt testing and evaluation
• LangSmith: LangChain’s evaluation platform
• Braintrust: Continuous evaluation for AI products
• Humanloop: Prompt management with built-in evals

Resources

• Promptfoo Documentation
• Anthropic Evaluation Guide

Why Guardrails Matter

The Risks

• Prompt injection: Malicious inputs that hijack model behavior
• Jailbreaking: Bypassing safety guidelines
• Data leakage: Exposing sensitive information in outputs
• Harmful content: Generating inappropriate or dangerous responses

Industry Reality

• Every production AI system needs guardrails
• Regulatory requirements increasing (EU AI Act, state laws)
• Reputational risk from AI failures

Input Guardrails

Techniques

1. Input Validation

def validate_input(user_input: str) -> bool:
    # Length limits
    if len(user_input) > 10000:
        return False

    # Known injection patterns
    injection_patterns = ["ignore previous", "disregard instructions", "system:"]
    if any(pattern in user_input.lower() for pattern in injection_patterns):
        return False

    return True

2. Content Classification

# Use a classifier model to check input safety
safety_check = classifier.predict(user_input)
if safety_check["harmful_probability"] > 0.8:
    return "I cannot process this request"

Output Guardrails

Techniques

1. Schema Validation

from pydantic import BaseModel, validator

class SafeResponse(BaseModel):
    answer: str

    @validator('answer')
    def no_pii(cls, v):
        # Check for patterns like SSN, credit cards
        if re.search(r'\d{3}-\d{2}-\d{4}', v):
            raise ValueError("Response contains potential PII")
        return v

2. Amazon Bedrock Guardrails

response = bedrock.invoke_model(
    modelId="anthropic.claude-sonnet-4-20250514-v1:0",
    guardrailIdentifier="your-guardrail-id",
    guardrailVersion="1",
    body=json.dumps({"messages": messages})
)

Defense in Depth: The Guardrail Stack

Layered Protection

┌─────────────────────────────────────────┐
│  Layer 1: Input Validation              │
│  - Length limits, format checks         │
├─────────────────────────────────────────┤
│  Layer 2: Content Moderation            │
│  - Pre-flight safety classification     │
├─────────────────────────────────────────┤
│  Layer 3: System Prompt Hardening       │
│  - Clear boundaries, role definitions   │
├─────────────────────────────────────────┤
│  Layer 4: Model-Level Safety            │
│  - Built-in model guardrails            │
├─────────────────────────────────────────┤
│  Layer 5: Output Validation             │
│  - Schema enforcement, PII detection    │
├─────────────────────────────────────────┤
│  Layer 6: Human Review                  │
│  - High-stakes decisions flagged        │
└─────────────────────────────────────────┘

The Long Context Era (2026)

Available Context Windows

The Challenge

• Having long context ≠ Using it effectively
• “Lost in the middle” phenomenon still exists
• More context = more cost, more latency

Long Context Best Practices

Strategies for Effective Use

1. Put Critical Information at Start and End

<critical_instructions>
[Most important rules here - model attends strongly]
</critical_instructions>

<context>
[Supporting documents, examples, background]
</context>

<task>
[Current request - model attends strongly]
</task>

2. Use Explicit Section Markers

<document id="1" relevance="high">...</document>
<document id="2" relevance="medium">...</document>

3. Summarize When Possible

• Don’t dump 50 pages when a 2-page summary suffices
• Use hierarchical summarization for very long documents

When to Use Long Context vs. RAG

Decision Framework

Hybrid Approach (Best of Both)

1. RAG for retrieval: Find relevant chunks
2. Long context for reasoning: Include full retrieved documents
3. Result: Precise retrieval + comprehensive understanding

Case Study 1: Stripe - Agentic Commerce Suite

The Challenge

• Enable AI agents to conduct commerce on behalf of users
• Manage fragmented integrations across different AI platforms
• Secure payment credential handling

The Solution (December 11, 2025)

• Single Integration: Sell through multiple AI agents with one integration
• Shared Payment Tokens: AI agents securely transmit buyer credentials to merchants
• Agentic Commerce Protocol (ACP): Open standard for AI-driven commerce

Adoption

Major retailers: Coach, Kate Spade, URBN, Revolve, Ashley Furniture Platforms: Squarespace, Wix, Etsy, WooCommerce, BigCommerce

Source: Stripe Agentic Commerce Suite

Case Study 2: Notion 3.0 - AI Agents with Context Engineering

The Challenge

• AI needs to understand user’s entire workspace
• Multi-step workflows requiring sustained context
• Integration with external tools

The Solution (September 18, 2025)

• 20+ minute multi-step actions with state-of-the-art memory system
• AI Connectors: Pull context from Slack, Google Drive, GitHub
• Custom Instructions Page: Agent learns your work style and preferences
• MCP Partnerships: Lovable, Perplexity, Mistral, HubSpot
• Built-in Models: Claude Sonnet 4, GPT-5, Gemini 3 Pro (no extra fees)

Customer Quotes

“We can now instantly spin up ready-to-use systems that used to take hours…” - Ben Levick, Ramp

“It’s like a coworker that’s been around and has genuine context.” - Harsha Yeddanupudy, Faire

Source: Notion 3.0: Agents

Case Study 3: Cursor - Fastest Growing SaaS Company

The Numbers (2025)

• 1M users, 360,000+ paying customers (within 16 months)
• $500M ARR (May 2025), up from $300M in April (~60% MoM growth)
• $2.6B valuation (January 2025)
• Fastest SaaS company from $1M to $500M ARR

Enterprise Adoption

• 25% of Fortune 500 companies pilot or deploy Cursor
• 40,000+ enterprise customers
• Used by OpenAI, Shopify engineers

Productivity Impact

• 126% productivity increase reported by users
• 40% faster debugging
• 25-35% reduction in development time
• 5x faster code completion than manual typing

Efficiency

• Only 40-60 employees
• $1.67M-$2.5M revenue per employee

Source: Cursor Statistics 2025

Advanced Prompting Techniques (2026)

Self-Consistency

• Generate multiple responses with temperature > 0
• Take majority vote or aggregate answers
• Reduces hallucination on reasoning tasks

Tree of Thoughts (ToT)

• Explore multiple reasoning paths
• Evaluate and prune branches
• Backtrack when stuck

Reflection Prompting

First, provide your answer.
Then, critically evaluate your answer for errors.
Finally, provide your corrected final answer.

Meta-Prompting

• Use one LLM call to generate/improve prompts for another
• “Write a prompt that would help an LLM solve this type of problem”

The Future: Agentic Context Engineering

ACE (Agentic Context Engineering)

• Latest research direction (2025-2026)
• Context evolves like a “playbook” that self-updates
• Models autonomously refine their prompts and memory

Key Trends

1. Dynamic Context: Adapts in real-time based on task
2. Self-Improving Systems: Learn from failures automatically
3. Multi-Agent Context Sharing: Agents coordinate context
4. Context as Code: Version-controlled, testable, reviewable

Industry Impact

• Enterprise AI spending: $37B in 2025 (up from $11.5B in 2024)
• Organizations with robust context architectures see:
  • 50% improvement in response times
  • 40% higher quality outputs

AI Coding Assistants: The Landscape

• Evolution: From OpenAI Codex & GitHub Copilot (autocomplete) to autonomous agents.
• Models: Powered by GPT-4o, Claude Sonnet 4, Claude Opus 4, Gemini 2.0 Pro.
• Main Categories:
  • Plugin-based: Extensions for existing IDEs (VS Code, JetBrains).
  • Agentic IDEs: Standalone editors reimagined for AI collaboration.

Category 1: Plugin-based Assistants

• Philosophy: Enhance your existing environment (VS Code, IntelliJ, Terminal).
• Examples:
  • GitHub Copilot: The industry standard for autocomplete & chat.
  • Aider: A CLI tool for pair programming; edits files directly via git.
  • Roo Code: VS Code extension enabling autonomous task execution.
  • Claude Code: Agentic CLI tool from Anthropic (often used alongside IDEs).

Category 2: Agentic IDEs

• Philosophy: Deeply integrated AI that “sees” the whole codebase and can drive the editor.
• Examples:
  • Cursor: A VS Code fork. Famous for “Composer” (multi-file edits) and “Tab” (prediction).
  • Windsurf: By Codeium. Features “Cascade” flow and deep context awareness.
  • Antigravity: Advanced agentic coding environment (Google).

Comparative Analysis

Spotlight: Google Antigravity

• What is it?: An agent-first IDE from Google DeepMind (announced Nov 2025).
• Pricing: Free for individuals with a personal Gmail account (public preview).
  • Access to Gemini 3 Pro/Flash, Claude Sonnet/Opus 4.5, GPT-OSS-120b.
  • Unlimited tab completions and generous weekly rate limits.
• Key Differentiator: Multi-agent orchestration via “Agent Manager”.

Antigravity: Core Capabilities

• Agent-First Paradigm: AI agents autonomously plan, execute, validate, and iterate.
• Multi-Agent Orchestration: Spawn multiple agent threads working in parallel (e.g., refactor + test).
• Comprehensive Interaction: Agents control editor, terminal, and browser.
• Artifacts for Trust: Produces rich markdown, diagrams, browser recordings, and diffs for human review.
• VS Code Fork: Familiar interface with an agent sidebar.

MCP Integration with AI Coding Assistants

• What is MCP?: Model Context Protocol (Anthropic) — an open standard for connecting LLMs to external data and tools.
• Why it Matters: Transforms AI from static knowledge to dynamic agents with real-time context.
• Supported Tools:
  • Claude Code: Native MCP support for databases, APIs, and custom tools.
  • Cursor: Configure MCP servers in settings to connect to external systems.
  • Antigravity: Integrates with Google Workspace, GitHub, Slack via MCP-like connectors.

MCP Use Cases in Development

• Database Queries: AI can directly query your Postgres/MySQL via MCP servers (e.g., Supabase MCP, Firebase MCP).
• API Integration: Connect to REST APIs, Slack, Notion, or GitHub for richer context (GitHub MCP, Notion MCP).
• Documentation Access: Context7 MCP provides up-to-date, version-specific docs for ~20,000 libraries (prevents hallucinations).
• Design-to-Code: Figma MCP extracts design context and generates code from Figma files.
• Browser Automation: Playwright MCP and Chrome DevTools MCP enable AI to control browsers for testing and debugging.
• Custom Tools: Build your own MCP servers to expose proprietary data or internal tools.

Example MCP Workflow

• Scenario: Developer asks: “Find all users who signed up last week.”
• Steps:
  1. Claude Code (via Supabase MCP) queries the database and returns results.
  2. Developer: “Generate a CSV export.”
  3. Agent writes the script and executes it.
• Benefit: No context switching between IDE, database UI, and documentation.

Spotlight: Claude Code Architecture

The Complete Claude Code Stack (Boris Cherny)

Claude Code Architecture

Source: Boris Cherny on X

CLAUDE.md: The Project Brain

What is CLAUDE.md?

• Persistent context that Claude automatically incorporates into every conversation
• Solves the problem of repeatedly explaining the same context
• Think of it as a configuration file for your AI pair programmer

File Hierarchy

~/.claude/CLAUDE.md              # Global (all projects)
~/repos/org/CLAUDE.md            # Organization-wide
~/repos/org/project/CLAUDE.md    # Project-specific (most common)
~/repos/org/project/src/CLAUDE.md  # Subdirectory (additive)

Key Insight: Files are additive - subdirectory CLAUDE.md appends to parent, doesn’t override.

CLAUDE.md: What to Include

Essential Sections

# Project Overview
This is a FastAPI e-commerce backend with Stripe integration.

# Tech Stack
- Python 3.12, FastAPI, SQLAlchemy 2.0
- PostgreSQL 15, Redis for caching
- pytest for testing

# Commands
- Run tests: `uv run pytest`
- Start dev server: `uv run uvicorn main:app --reload`
- Lint: `uv run ruff check --fix . && uv run ruff format .`

# Code Style
- Use Pydantic for all data validation
- Private functions start with underscore
- One parameter per line in function signatures

# Architecture Decisions
- All database queries go through repository pattern
- Use dependency injection for testability

CLAUDE.md: Best Practices

Do’s

1. Keep it concise - ~150-200 instructions max (frontier model limit)
2. Focus on the “how” - Commands, patterns, conventions
3. Use /init - Let Claude generate a starter, then refine
4. Update regularly - Treat as living documentation

Don’ts

1. Don’t auto-generate - Manually craft for best results
2. Don’t dump everything - Use progressive disclosure
3. Don’t include obvious things - Claude already knows Python syntax

Pro Tip: Progressive Disclosure

# For detailed API documentation, see: docs/api/README.md
# For database schema details, see: docs/schema.md

Tell Claude where to find information, not all the information itself.

Skills: Modular Expertise

What are Skills?

• Modular chunks of CLAUDE.md that load only when needed
• Follow the Agent Skills open standard
• Can include scripts, templates, and supporting files

Skill Structure

.claude/skills/
├── deploy/
│   ├── SKILL.md           # Skill definition
│   ├── deploy.sh          # Supporting script
│   └── config.template    # Template file
├── review-pr/
│   └── SKILL.md
└── database-migrate/
    └── SKILL.md

SKILL.md Example

---
invocation: explicit      # Only when user calls /deploy
context: fork             # Run in isolated subagent
agent: general-purpose    # Which agent to use
---

# Deploy to Production

Follow these steps to deploy:
1. Run tests: `uv run pytest`
2. Build: `docker build -t app .`
3. Push: `docker push registry/app`
4. Deploy: `kubectl apply -f k8s/`

Skills: Invocation Modes

Three Ways Skills Activate

Custom Commands = Skills

.claude/commands/fix-issue.md  →  /project:fix-issue
.claude/skills/fix-issue/SKILL.md  →  /fix-issue

Both create commands! Skills add: directories, frontmatter, subagent support.

Passing Arguments

/project:fix-github-issue 1234

In fix-github-issue.md:

Fix GitHub issue #$1
First, read the issue details...

Subagents: Isolated Workers

What are Subagents?

• Isolated Claude instances with their own context window
• Delegate entire tasks, get results back
• Keep main conversation context clean

Architecture

┌─────────────────────────────────────────────────────────┐
│  Main Claude Session                                    │
│  ┌───────────────────────────────────────────────────┐  │
│  │ Your conversation history + CLAUDE.md context     │  │
│  └───────────────────────────────────────────────────┘  │
│                         │                               │
│            ┌────────────┴────────────┐                  │
│            ▼                         ▼                  │
│  ┌─────────────────┐      ┌─────────────────┐          │
│  │ Subagent: Explore│      │ Subagent: Plan  │          │
│  │ (Read-only)      │      │ (Architecture)  │          │
│  │ Own context      │      │ Own context     │          │
│  └────────┬─────────┘      └────────┬────────┘          │
│           │                         │                   │
│           └─────────┬───────────────┘                   │
│                     ▼                                   │
│           Results returned to main                      │
└─────────────────────────────────────────────────────────┘

Subagents: Built-in Types

Available Subagents

Using Subagents in Skills

---
context: fork           # Creates isolated subagent
agent: Explore          # Use Explore agent type
---

# Find Authentication Code
Search the codebase for all authentication-related files.
Look for: login, logout, JWT, session, auth middleware.

Why Use Subagents?

1. Context efficiency - Don’t pollute main conversation
2. Parallel execution - Multiple subagents can work simultaneously
3. Safety - Explore agent can’t modify files

Hooks: Deterministic Automation

What are Hooks?

• Shell commands that trigger automatically during Claude Code events
• Programmable checkpoints for validation, formatting, integration
• The “must-do” rules that complement CLAUDE.md “should-do” suggestions

Hook Lifecycle

┌─────────────────────────────────────────────────────────┐
│                    Claude Code Events                    │
├─────────────────────────────────────────────────────────┤
│                                                         │
│  SessionStart ──► User types prompt                     │
│       │                                                 │
│       ▼                                                 │
│  UserPromptSubmit ──► Claude processes                  │
│       │                                                 │
│       ▼                                                 │
│  PreToolUse ──► [HOOK: Validate/Modify] ──► Tool runs  │
│       │                                                 │
│       ▼                                                 │
│  PostToolUse ──► [HOOK: Format/Log] ──► Continue       │
│       │                                                 │
│       ▼                                                 │
│  Notification ──► [HOOK: Alert user]                   │
│       │                                                 │
│       ▼                                                 │
│  Stop ──► Agent completes response                     │
│                                                         │
└─────────────────────────────────────────────────────────┘

Hooks: Configuration

Hook Types and Exit Codes

Configuration in settings.json

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "echo 'About to modify: $TOOL_INPUT'"
          }
        ]
      }
    ],
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "ruff format $FILE_PATH"
          }
        ]
      }
    ]
  }
}

Hooks: Practical Examples

Auto-Format on Every Edit

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|MultiEdit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "if [[ $FILE_PATH == *.py ]]; then ruff format $FILE_PATH; fi"
          }
        ]
      }
    ]
  }
}

Block Dangerous Operations

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "if echo $TOOL_INPUT | grep -q 'rm -rf'; then exit 1; fi"
          }
        ]
      }
    ]
  }
}

Slack Notification on Completion

{
  "hooks": {
    "Notification": [
      {
        "matcher": ".*",
        "hooks": [
          {
            "type": "command",
            "command": "curl -X POST -d '{\"text\":\"Claude needs attention\"}' $SLACK_WEBHOOK"
          }
        ]
      }
    ]
  }
}

Claude Code: Resources

Official Documentation

• Claude Code Docs
• CLAUDE.md Guide
• Skills Reference
• Hooks Reference

Community Resources

• Awesome Claude Code - Curated skills, hooks, plugins
• Claude Code Best Practices - Official Anthropic guide
• The Complete Guide to CLAUDE.md

Key Insight

“Hooks are huge and critical for steering Claude in a complex enterprise repo. They are the deterministic ‘must-do’ rules that complement the ‘should-do’ suggestions in CLAUDE.md.”

Spotlight: Google Antigravity

What is Antigravity?

• Agent-first IDE from Google DeepMind (announced Nov 2025)
• VS Code fork with deep AI integration
• Free for individuals during public preview

Key Differentiators

Performance

• SWE-bench Verified: 76.2% (1% behind Claude Sonnet 4.5)
• Terminal-Bench 2.0: 54.2% (vs GPT-5.1’s 47.6%)

Download

• antigravity.google - macOS, Windows, Linux

Spotlight: AWS Kiro

What is Kiro?

• Agentic IDE + CLI from AWS
• Spec-driven development with agent hooks and “powers”
• Free tier available - 500 bonus credits for new users

Kiro CLI Installation

# macOS (Homebrew)
brew install --cask kiro-cli

# Linux (one-liner)
curl -fsSL https://kiro.dev/install.sh | sh

# Verify installation
kiro-cli --version

Getting Started

# Login with AWS Builder ID, GitHub, or Google
kiro-cli auth login

# Start interactive chat
kiro-cli chat

# Select model (Auto recommended)
# Options: Auto (1x), claude-sonnet-4.5 (1.3x), claude-haiku-4.5 (0.4x)

Key Features

• Steering files - Similar to CLAUDE.md
• MCP integration - Connect external tools
• Powers - Modular agent capabilities
• Works with Kiro IDE - Shared configuration

Resources

• Kiro Downloads
• Kiro CLI Docs
• Kiro FAQ

Technique: Spec-Driven Development

• The Problem: Vague prompts lead to hallucinated or poor code.
• The Fix: Plan First / Code Later.
• Process:
  1. Draft a Spec: Create a markdown file describing requirements (API, Data Models).
  2. Human Review: You review the design.
  3. Agent Reflection: Ask the LLM: “Review this spec for edge cases or security flaws.”
  4. Execute: Only generate code once the plan is solid.

Technique: Team Persona

• Concept: Simulate a full engineering team.
• Prompting Strategy:
  • “Act as a Product Manager: Are requirements clear?”
  • “Act as a Frontend Engineer: Is the UI UX-friendly?”
  • “Act as a Backend Engineer: Is the DB schema normalized?”
  • “Act as Infra/SRE: How do we deploy this?”
• Benefit: Catch issues across different concerns before writing code.

References and Further Reading

References: Foundational Papers

• Brown et al. (2020). “Language Models are Few-Shot Learners.” GPT-3 Paper
• Wei et al. (2022). “Chain of Thought Prompting Elicits Reasoning in Large Language Models.” link
• Min et al. (2022). “Rethinking the Role of Demonstrations: What Makes In-Context Learning Work?” link
• Touvron et al. (2023). “LLaMA: Open and Efficient Foundation Language Models.” link

References: Context Engineering & DSPy

Context Engineering

• Context Engineering Guide - Prompting Guide
• From Prompt Engineering to Context Engineering
• Context Engineering: A Complete Guide 2026

DSPy Framework

• DSPy Official Site
• GitHub: stanfordnlp/dspy
• DSPy Tutorial 2025

References: Prompt Engineering by Model

Evaluation & Testing

• Promptfoo Documentation
• Anthropic Evaluation Guide

References: AI Coding Assistants

Claude Code

• Claude Code Docs
• CLAUDE.md Guide
• Skills Reference
• Hooks Reference
• Claude Code Best Practices
• The Complete Guide to CLAUDE.md
• Awesome Claude Code

Other Tools

• Cursor | Cursor Statistics
• AWS Kiro | Kiro CLI Docs
• Google Antigravity
• Aider
• Roo Code

References: Industry Case Studies

• Stripe Agentic Commerce Suite (Dec 2025)
• Notion 3.0: Agents (Sep 2025)
• Cursor Adoption Trends

Code Samples

• Prompt Engineering Examples